The ability to heal wounds and regenerate lost body parts is of fundamental importance to many animals. Because regeneration and embryogenesis share a common developmental endpoint, it has been suggested that regeneration may in part re-deploy embryonic developmental processes. Many annelid worms have extensive regenerative abilities and experimentally tractable embryos, providing an excellent opportunity to explore the relationships between regenerative and embryonic development. The primary objective of this proposal is to investigate the relationship, at both the cellular and molecular levels, between regeneration and embryogenesis in the annelid Tubifex. Studies will focus on the development of segments, the fundamental body units of annelids, with particular attention to the nervous system. The three specific aims of the project are: 1) to determine whether cell lineage contributions in regenerated segments are the same as those in embryonically produced segments; 2) to determine whether embryonically produced segments made aberrant through teloblast ablation can produce normal segments through regeneration; 3) to characterize and compare the molecular processes of segment formation during regeneration and embryogenesis.